1. Field of the Invention
The present invention relates to an electrical signal regulator circuit, such as a voltage-regulator circuit, for example, or a regulator circuit for a glass unit to protect the glass unit from damage.
2. Related Art
Glass units may be heated to reduce fogging, condensation or other accumulation of moisture. They may also be heated after the glass has become fogged in order to eliminate any accumulated condensation. Glass units such as those for refrigeration units in commercial establishments, such as grocery stores and convenience markets, are often heated to minimize any fogging or condensation of ambient humidity.
Refrigerator doors, for example, are commonly coated with a resistive material to which is applied a voltage to heat the material and thereby the glass, reducing or eliminating any condensate, or the potential for moisture to condense on the glass. These coatings are sometimes referred to as transparent conductors, and are applied to one surface of the glass. The transparent conductor has an inherent fixed resistivity, and the resistance of a given coating depends on the bulk resistivity and thickness of the coating and the size of the glass on which the coating is placed. The amount of heat produced in the coating for a given glass unit then depends on the applied voltage which, in accordance with conventional applications is most conveniently and economically the line voltage available from the electric utility. In the United States, the line voltage is 120 volts while the line voltage in Europe is 220/240 volts. Therefore, glass doors or other glass units to be used in the United States are coupled to control circuits designed for operation at 120 volts. Units to be used in Europe use control circuits designed for 220/240 volts. Considering glass units for the United States, then, the heating of such glass units depends on the door or glass size and the bulk resistivity and thickness of the coating as to how much the glass is to be heated. Thus, for a given environment, a larger door will have a different thickness to achieve the necessary heat production than a smaller door, for the conventional line voltage. For a given size door, a glass unit used in a humid area would require more heat to avoid fogging than would a glass unit used in an arid area. Therefore, a glass unit for a humid area optimally should be coated with less material than one for an arid area. In practice however, a coating typically is applied to a glass unit so that the glass unit can be used in any area, regardless of the humidity and ambient temperature.
The relationship between the door size, resistivity and voltage derives from the bulk resistivity of the material and the thickness of the material applied to the door, which translates into a resistance per square, wherein the area is a dimensionless quantity. The voltage to be used is derived from the power equation P=I.sup.2 .times.R, wherein "P" is the power, "I" the current and "R" the resistance, the latter being determined by the size of the door, assuming a predetermined resistance per square. The voltage V will then be the square root of the product of "P" and "R".
Glass units can now be produced economically with a uniform thickness of a given transparent conductor (i.e., a standard resistance per square), giving rise to the need for a means for applying the proper voltage to a glass unit for a given unit size, and also preferably as a function of the surrounding environment. There is a need for a reliable, low-cost, and predictable method of applying voltage to the transparent conductive coating on such glass units in a known amount and character.